Process of making tanning extracts.



UNITED STATES Patented May 12, 1903.

QATENT OFFICE.

PROCESS OF MAKING TANNING EXTRACTS.

SIECIFIGATION forming part of Letters Patent No. 727,798, dated May 12,1903;

' Application filed November 5, 1901. Serial No. SL253. (No specimens.)

To all whom it may concern:

Be it known that I, MAX Home, a subject of the Emperor ofAustria-Hungary, residing at Briinn, in the Province of Moravia, intheEmpire of Austria-Hungary, have invented certain new and usefulImprovements in Processes of Making Tanning Extracts; and I do herebydeclare the following to be a full, clear, and exact description of theinvention, such as will enable others skilled in the art to which itappertains to make and use the same.

My invention has relation to the production or formation of a tanningagent from the Waste lyes resulting from the manufacture of cellulose bythe sulfite process.

In the production of tanning agents from I the waste sulfite lyesreferred to by the processes made use of prior to my invention thetanning condensate obtained is of a very dark color, the leather beingof agray-black color, which is, commerciallyspeaking, undesirable, whileon the other hand the leather is rendered very brittle. This isespecially the case when the waste lyes are neutralized beforeconcentration by means of milk of lime for the purpose of eliminatingthe combined and free sulfurous'acid, as it is well known that solutionsof tannin or tannic acid in the presence of alkaline carbohydratesundergo rapid changes and become very dark. I have found that even wherestrong mineral acids are used for eliminating the sulfurous acid,removing the latter by evaporation or by blowing air through the lye, itis practically impossible to prevent or solimit the changes abovereferred to as to obtain a tanning agent soluble in water and forminglight -colored clear solutions wherewith leather can be tanned and thetanned leather possess the usual light yellow-brown color. I came to theconclusion that if it were possible either to prevent or suflicientlycounteract the changes in color which the tanning constituent undergoesin the lye, and thereby prevent its becoming so deeply colored as torender its use for tanning leather practically of little value, aproduct could be obtained of great con1- mercial value. I havediscovered that this result can be attained and the disadvantages knownprocesses and above referred to entirely obviated. This resultl attainby bleaching the lye before concentration, and as hydrosulfurous acid isa well known and powerful bleaching agent I make use of the combined andfree sulfurous acid present in the lyes byconvertingitintohydrosulfurous acid, whereby the lye is sufficiently bleached to obtaina condensate of the desired depth of color and one that is soluble inWater.

That my invention may be fully understood, I will describe the same indetail.

Broadly speaking, the process consists, essentially, in reacting uponthe waste sulfite lye with an acid capable of liberating the combinedsulfurous acid and the acetic acid in the lye without injnrionslyafiecting the tanning constituents therein and with a sufficiency ofzinc to convert the whole or substantially the whole of the sulfurousacid in the lye into hydrosulfurous acid.

In practice I prefer to proceed as follows: The percentage of free andcombined sulfurous acid in the lye is determined, a quantity of zinc inthe form of dust sufficient to convert both the free and combinedsulfurous acid into hydrosulfurous acid is added to the lye while beingstirred, and then the acid capable of liberating the combined sulfurousand acetic acid-as, for instance, sulfuric, phosphoric,or oxalic acid-ispreferably gradually added to gradually liberate the combined acetic andsulfurous acid, the latter to be gradually reacted upon by the zinc and,together with the free sulfurous acid, converted into hydrosulfurousacid, the lye being agitated until the conversion is completed, theprocess being carried out at normal temperatures and, if necessary,under the influence of a cooling agent to keep the temperatu re of thelye down-to about 30 centigrade.

To convert sulfurous acid into hydrosulfurous acid, one molecule of Znfor every two molecules of S0 is required, the reaction being awell-known one. Taking, for instance,

a waste cellulose sulfite lye containing, per liter, sulfurous andacetic acid in the 'following proportions: sulfurous acid, free, 1.928

(C H O QH so 1406 a: 2.153 grams sulfuric acid. 1; "00 2 z 4 9 2.013 x1.644 grams.

3.797 grams sulfuric acid.

Hence to convert the whole of the sulfurous acid (1.928+1.4@O6) 1.693grams zinc powder will be required according to the conversion equation.An additional quantity of acid can of course be added to the lye if theremainder of the lime, which is chiefly combined with organic acid, isto be precipitated. This can, however, also be effected by using asufficient quantity of a salt that Will combine and form Withthe lime aninsolublecompound bydouble decomposition as, for instance, a sulfate,phosphate or oxalate, and the like-the insoluble lime compound beingremoved by filtration-as, for instance, in a filter-pressthe lye beingthen concentrated to the proper degree by evaporation. The concentrationmay be carried out in a single-efiect evaporator; but in this case theseparation of the crystalline sulfate, phosphate, or oxalate of limetakes place, resulting in hammering, while the insoluble lime compounddeposits upon the heating-pipes, which is of course undesirable. Toavoid this, I effect the concentration in a double-effect evaporator byfirst evaporating the lye to from 16 to 18 Baum, after which I removethe insoluble calcium compounds by filtration and finally condense thelye in vacuum to from 28 to 30 Baum.

Although phosphoric acid has the same property as sulfuric acid andoxalic acid in that, like the last-named two acids, it will liberate thecombined acetic and sulfurous acids in the lye, yet it has not theproperty of precipitating calcium, so that when phosphoric acid is usedthe removal of the calcium can be effected by converting it into aninsoluble salt, as hereinabove described.

It is of course evident in carrying out my invention that it isimmaterial whether the sulfite lye is first reacted upon with anacidreversed and the solution first treated with zincand then with theacid.

Having thus described my invention, what I claim as new therein, anddesire to secure by Letters Patent, is-

1. The process, which consists in reacting upon a waste lye, resultingfrom the manufacture of cellulose by the sulfite process,with zinc toconvert the sulfurous acid present into hydrosulfurous acid, andliberating the combined sulfurous acid and the combined acetic acid inthe lye by means of an acid indifiercut to the tanning constituentspresent, for the purpose set forth.

2. The process, which consists in reacting upon a waste lye, resultingfrom the manufactu re of cellulose by the sulfitc process,with zinc toconvertthe sulfurous acid into hydrosulfurous acid, and with an acidindifferent to the tanning constituents and capable of liberating thecombined sulfurous acid as Well as the combined acetic acid present, andprecipitating the calcium, for the purpose set forth.

3. The process, which consists in reacting upon a Waste lye, resultingfrom the manufacture of cellulose by the sulfite process,with zinc toconvert the sulfurous acid present into hydrosulfurous acid, andtreating the lye, during conversion, with sulfuric acid to liberate thecombined sulfurous acid, as well as the combined acetic acid, for thepurpose set forth.

4. The process, which consists in reacting upon a waste lye, resultingfrom the manufacture of cellulose by the sulfite process,with zinc toconvert thesulfurous acid present into hydrosulfurous acid, treating thelye, during conversion, with an acid indifierent to the tanningconstituents and capable of liberating the combined sulfurous acid aswell as the combined acetic acid present, and reacting upon the lye witha salt capable of combining and forming with the calcium present aninsoluble calcium compound, for the purposes set forth.

In testimony that I claim the foregoing as my invention I have signed myname in presence of two subscribing witnesses. U

' MAX l-IONIG.

Witnesses:

W. DRAHOKOUPIT, WOLF DREW.

